Fibers, ignitible

In flame retarding nonwovens, the contribution of components may not be additive. Rather, the interaction of binder, flame retardant, and substrate is critical in the performance of the flame retardant nonwoven. Similarly, the flammability of a binder film or the flammability of a flame retardant coated woven cloth often do not predict the flame retardancy of the same binder or flame retardant on a nonwoven substrate of rayon or polyester. Actual data on a nonwovens substrate is the only accurate measure of a system s flame retardancy. For this study, two widely used substrates were selected. The first, lightweight rando rayon, is representative of material used in nurse caps, surgeon s masks, and miscellaneous coverstock. This material is constructed of 1 1/2 denier fiber, weighs 1 1/2 ounces per square yard, and is relatively dense web. Rayon as a material is water absorbent, burns rather than melts, and is readily flammable. This fiber ignites around 400°C(2) and has an oxygen index of about 19.0. Certain binders adhere well to rayon while others do not. Apparently, this lack of affinity for the substrate affects flame retardancy, as will be demonstrated later. 

Hazard Toxic by inhalation. TLV (dust) 0.2 mg/m3. Moderately flammable in the form of dust or linters fiber ignites readily. In the form of dust or linters, exposure of workers in textile mills may cause brown lung. ... 

Although this first route was simple in concept, it proved slow in operation, difficult to scale up safely, and relatively uneconomical compared with the other routes. Denitration of the fibers, necessary to allow safe use wherever the fabrics may risk ignition, spoiled their strength and appearance. Nevertheless, Chardoimet earned and truly deserved his reputation as the Eather of Rayon. His process was operated commercially until 1949 when the last factory, bought from the Tubize Co. in the United States in 1934 by a Bra2iUan company, burned down. 

Thermal Properties. Fibers are not thermoplastic and stable to temperatures below 150°C, with the possible exception of slight yellowing. They begin to lose strength gradually above 170°C, and decompose more rapidly above 300°C. They ignite at 420°C and have a heat of combustion of 14,732 J/g (3.5 kcal/g). 

Thermoplastic Fibers. The thermoplastic fibers, eg, polyester and nylon, are considered less flammable than natural fibers. They possess a relatively low melting point furthermore, the melt drips rather than remaining to propagate the flame when the source of ignition is removed. Most common synthetic fibers have low melting points. Reported values for polyester and nylon are 255—290°C and 210—260°C, respectively. 

F. P. McCuUough and B. C. Goswami, "Novel Fibers and Their Ignition Behavior," Hi-Tech Conference, Clemson University, S.C., July 21,1993. 

Chemical Hazards. Chemical manufacturers and employees contend with various ha2ards inherent ia productioa of evea commonplace materials. For example, some catalysts used ia the manufacture of polyethylene (see Olefin polymers) ignite when exposed to air or explode if allowed to become too warm the basic ingredient ia fluorocarboa polymers, eg, Tefloa (see Fluorine compounds, organic), can become violently self-reactive if overheated or contaminated with caustic substances (45,46) one of the raw materials for the manufacture of acryflc fibers (see Fibers, acrylic) is the highly toxic hydrogen cyanide (see Cyanides). 

Scope—Articles 500 Through 505. Articles 500 through 505 cover the requirements for electrical equipment and wiring for all voltages in locations where fire or explosion hazards may exist due to flammable gas or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings. 

Equipment shall be approved not only for the class of location but also for the explosive, combustible, or ignitable properties of the specific gas, vapor, dust, fiber, or flyings that will be present. In addition. Class I equipment shall not have any exposed surface that operates at a temperature in excess of the ignition temperature of the specific gas or vapor. Class II equipment shall not have an external temperature higher than that specified in Section 500-3(1). Class III equipment shall not exceed the maximum surface temperatures specified in Section 503-1. 

Class III Locations. Class III locations are those that are hazardous because of the presence of easily ignitable fibers or flyings, but in which such fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitable mixtures. Class III locations shall include those specified in (a) and (b) below. 

FPN No. 2) Easily ignitable fibers and flyings include rayon, cotton (including cotton linters and cotton waste), sisal or henequen, istle, jute, hemp, tow, cocoa fiber, oakum, baled waste kapok, Spanish moss, excelsior, and other materials of similar nature. 

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